After circuit boards have been manufactured but prior to the population of the boards with discrete electrical components and integrated circuits, it is common to test the circuits in the boards to ensure they have been properly formed.
Known devices for testing unpopulated circuit boards are generally divided into two groups: 1) devices using an adapter that contacts simultaneously to all circuit test points of the circuit board; and 2) so-called finger testing devices or finger testers that sequentially scan individual test points of the circuit boards using two or more test fingers.
Irrespective of the type of device involved, the individual circuits of the boards are tested for open-circuits and shorts. In open-circuit testing, the testing device determines whether an open circuit condition exists between two or more test point when the board's specifications dictate that the test points should be electrically connected. In short-circuit testing, the testing device determines whether an electrical connection exists between two or more test points when the board's specifications dictates that no electrical connection should exist. Typically, short circuit testing includes detection of both low and high impedance shorts.
Generally, both short-circuit and open-circuit testing are laborious and time-intensive processes. The presence or not of a short-circuit between each nominally discrete circuit must be determined, and each branch of a nominally single circuit must be tested for an open-circuit. In many modern circuit boards having a large number of separate and/or highly branched circuits, a high number of individual tests must be performed.
Attempts have been made to optimize the individual tests and to minimize the number needed to validate a given unpopulated circuit board. For example, short-circuit tests are performed with elevated voltages. Circuit boards thus tested tend to have high long-term reliability since the high voltage testing tends to exposed any transient short between the individual circuits. Testing only with conventional low test voltages make it nearly impossible to detect pseudo-shorts resulting from crosstalk between two circuits.